Atomic layer etching in continuous plasma

ABSTRACT

Methods and apparatus for etching substrates using self-limiting reactions based on removal energy thresholds determined by evaluating the material to be etched and the chemistries used to etch the material involve flow of continuous plasma. Process conditions permit controlled, self-limiting anisotropic etching without alternating between chemistries used to etch material on a substrate. A well-controlled etch front allows a synergistic effect of reactive radicals and inert ions to perform the etching, such that material is etched when the substrate is modified by reactive radicals and removed by inert ions, but not etched when material is modified by reactive radicals but no inert ions are present, or when inert ions are present but material is not modified by reactive radicals.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims benefit of U.S. Provisional Patent ApplicationNo. 62/322,135, filed Apr. 13, 2016, and titled “ATOMIC LAYER ETCHING INCONTINUOUS PLASMA,” and U.S. Provisional Patent Application No.62/292,115, filed Feb. 5, 2016, and titled “ATOMIC LAYER ETCHING INCONTINUOUS PLASMA,” which are incorporated by reference herein in theirentireties and for all purposes.

BACKGROUND

Plasma etch in atomic scale has been studied for many years.Conventional plasma etch processes are often performed at a high etchrate using reactive ions and reactive chemistry, but due to thereactivity of the plasma, the etching process often results in undesiredetch of layers under the material to be etched.

SUMMARY

Provided herein are methods and apparatus for etching substrates usingself-limiting reactions based on removal energy thresholds determined byevaluating the material to be etched and the chemistries used to etchthe material. Embodiments involve flow of continuous plasma at processconditions to permit controlled, self-limiting anisotropic etchingwithout alternating between chemistries used to etch material on asubstrate. According to disclosed embodiments, a well-controlled etchfront allows a synergistic effect of reactive radicals and inert ions toperform the etching, such that material is etched when the substrate ismodified by reactive radicals and removed by inert ions, but not etchedwhen material is modified by reactive radicals but no inert ions arepresent, or when inert ions are present but material is not modified byreactive radicals.

In one aspect, the disclosure relates to a method of etching a materialof a substrate. The method involves exposing a substrate in a processingchamber to both a plasma generated by a reactive species and a plasmagenerated by an inert ion gas to remove the material using self-limitingreactions, wherein the energy threshold for removing a layer of thematerial modified by the reactive species using the inert ion gas isless than the energy threshold for sputtering the material on thesubstrate using the inert ion gas. According to various embodiments,exposure of the substrate to the reactive species modifies the exposedsubstrate material, and the inert ions generated by the plasma removethe modified substrate material, thereby etching the substrate material.According to various embodiments, during the exposure of the substrateto the reactive species and inert ions, the plasma is deliveredcontinuously such that both source power and bias power are continuouslyon during the etch. And, according to various embodiments, theconcentration of inert gases present in the processing chamber duringthe etch is greater than 99% of all chemical species in the chamber,while the concentration of reactive species is less than about 1%.

In another aspect, the disclosure provides an apparatus for etching amaterial of a substrate, the apparatus having a controller to affect amethod of etching the material of the substrate in a processing chamberof the apparatus as described herein.

These and other aspects are described further below with reference tothe drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an energy diagram depicting energy thresholds relevant to adiscussion of atomic layer etching according to this disclosure.

FIGS. 2A-B are schematic illustrations of a substrate undergoingoperations of certain disclosed embodiments.

FIG. 3 is a process flow diagram depicting operations performed inaccordance with certain disclosed embodiments.

FIG. 4 is a schematic diagram of an example process etch chamber forperforming certain disclosed embodiments.

FIG. 5 is a schematic diagram of an example process apparatus forperforming certain disclosed embodiments.

FIG. 6 shows a plot of reference data of ion density and pressure forvarious inert gases relevant to a discussion of atomic layer etchingaccording to this disclosure.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth toprovide a thorough understanding of the presented embodiments. Thedisclosed embodiments may be practiced without some or all of thesespecific details. In other instances, well-known process operations havenot been described in detail to not unnecessarily obscure the disclosedembodiments. While the disclosed embodiments will be described inconjunction with the specific embodiments, it will be understood that itis not intended to limit the disclosed embodiments.

Atomic layer etching (ALE) is one approach for atomic scale control ofetching behavior. ALE is a technique for removing thin layers ofmaterials using sequential reaction steps that are self-limiting. Thismay be done by a surface modification operation (i.e. chemisorption byradical reaction of reactive chemistry on a substrate surface) followedby a removal operation (i.e. ion assisted etching using inert,non-reactive ions). Such operations may be repeated for a certain numberof cycles. During ALE, the reactive chemistry and the inert ions aredelivered separately to the substrate.

ALE has many advantages over traditional plasma etching for at leastsome etch applications. For example, ALE may be suitable for performinganisotropic etching, and may result in improved through-pitch loadingand aspect ratio dependence etching. ALE also generally results in lessdamage to the material to be etched and improved selectivity to a maskmaterial overlying the material to be etched.

However, ALE is usually slower than conventional plasma etching becausevery thin layers are etched in each ALE cycle and each cycle relies on asaturation curve wait time such that the modification chemistry hassufficient time to substantially saturate the surface of the material tobe etched. Saturation is also used during the removal operation, thusresulting in an extended process time. In addition, chemistries used inthe surface modification operation are different from chemistries usedin the removal operation, which, when performing ALE in alternatingpulses of modification chemistry and removal chemistry, increases thetime used to switch between chemistry flows to a chamber. Chemistriesare also often purged between pulses during each cycle to ensure aself-limiting reaction is performed in each cycle. The slower etch rateand process control difficulty with multiple gas changes in one cyclecan limit the use of ALE in semiconductor fabrication. ALE is also oftenperformed using simpler chemistry to reduce the likelihood of chemistrybuildup on the substrate to be etched. For example, more complexmolecules may not be suitable for use with ALE because such moleculesmay build up on the surface of the material to be etched and will notcompletely saturate the surface to perform a self-limiting etch process.

Disclosed methods of etching substrates use self-limiting reactionsbased on removal energy thresholds determined by evaluating the materialto be etched and the chemistries used to etch the material. Embodimentsinvolve flow of continuous plasma at process conditions to permitcontrolled, self-limiting anisotropic etching without alternatingbetween chemistries used to etch material on a substrate.

Disclosed embodiments performed using continuous plasma combine thebenefits of both ALE and regular continuous plasma etching. Plasmagenerated in disclosed embodiments includes reactive species (e.g.,radicals or molecules) and inert ions as etchants, while maintaining alow reactive ion density such that any etching effect of reactive ionsis negligible. As described herein, inert ions refer to ions of gasessuch as helium or argon that have sufficient energy to remove modifiedmaterial on the surface of the substrate but are not reactive enough toetch unmodified material itself. Additionally, reactive ion densityrefers to the density of ions, such as oxygen or chlorine ions, that arereactive such that they may etch the material on the substrate. Incontrast, reactive species, reactive radicals or reactive chemistry asdescribed herein may refer to the plasma species without charge used toreact with the material on the surface of the substrate to modify thesurface of the substrate.

In some embodiments, the concentration of inert gases present in thechamber may be greater than about 99% of all chemical species in thechamber, while the concentration of reactive species (e.g., modificationchemistry) may be less than about 1%. In some embodiments, high pressureplasma generates enough radical density of the reactive species evenwith their low concentration to modify the substrate, while maintainingan extremely low concentration of reactive ions at the substrate, due tothe low concentration and shorter mean-free-path in high pressure,thereby maintaining a high chemisorption rate and an etch rate fasterthan that of ALE.

In various embodiments, a low bias power (e.g., about 50 Vb) may beapplied during the etch process. In some embodiments, the bias power ispulsed, such as between 0 Vb and about 50 Vb. It will be understood thatthe terms “bias power” and “bias voltage” are used interchangeablyherein to describe the voltage for which a pedestal is set when a biasis applied to the pedestal. A threshold bias power or threshold biasvoltage refers to the maximum voltage of the bias applied to a pedestalbefore material on the surface of a substrate on the pedestal issputtered. The threshold bias power therefore depends in part on thematerial to be etched, the gas used to generate plasma, plasma power forigniting the plasma, and plasma frequency. Bias power or bias voltage asdescribed herein is measured in volts, which are indicated by the unit“V” or “Vb”, where b refers to bias.

According to disclosed embodiments, a well-controlled etch front allowsa synergistic effect of reactive radicals and inert ions to perform theetching, such that material is etched when the substrate is modified byreactive radicals and removed by inert ions, but not etched whenmaterial is modified by reactive radicals but no inert ions are present,or when inert ions are present but material is not modified by reactiveradicals. Disclosed embodiments reduce damage to the substrate from ionsand plasma, while maintaining high etch selectivity and smooth etchprofiles. In various embodiments, the sidewalls of features to be etchedmay not need to be passivated because process conditions are controlledby varying chamber pressure, concentration of inert ions, concentrationof reactive species, plasma power, plasma frequency, temperature, andexposure time such that there is little or no lateral etching orundercutting. Disclosed embodiments also reduce loading effects ormicroloading because process conditions are controlled to maintainself-limiting reactions at the surface of the substrate. Although theremay be some loading effects due to the process involving continuousetching and diffusion rates of the reactive species and the inert ionsin features of various sizes, the etching process may be controlled bypulsing the bias and controlling the duration of exposure to balance theetch rate between larger and smaller critical dimension features.

FIG. 1 shows an energy diagram depicting energy thresholds E₁, E₂, andE₃ relevant to a discussion of atomic layer etching according to thisdisclosure. Etch chemistries and process conditions for performingdisclosed embodiments are selected based on three energy thresholds: (1)E₁, the energy threshold needed to remove a modified material from thesurface of the material, (2) E₂, the energy threshold upon which inertions have sufficient energy to bombard or sputter onto the surface ofthe material to be etched (or material underlying the material to beetched), thereby resulting in physical removal of material on thesubstrate; and optionally (3) E₃, the energy threshold upon which inertions have sufficient energy to bombard or sputter onto the surface of amask layer over the target layer, thereby resulting in physical removalof mask material. FIG. 1 is an energy diagram depicting the region(between E₁ and E₂) within which disclosed embodiments are capable ofbeing performed to utilize the benefits of self-limiting etching whilereducing damage to the substrate and maintaining etch selectivity.

Process conditions and etch chemistries are selected such that E₁ isless than E₂, and if the material to be etched is under a patterned mask(as opposed to material to be etched being a blanket layer), processconditions and etch chemistries are also selected such that E1 is lessthan both E2 and E3. Such energy thresholds are selected to ensure thatinert ions have sufficient energy to remove modified material from thesurface (energy must be greater than E₁), but that inert ions do notsputter the surface of the material to be etched (energy must be lessthan E₂), and, in the case of etching to pattern a substrate, that inertions do not sputter or cause damage to the mask (energy must be lessthan E₃).

Disclosed embodiments can also be applied to many different andcomplicated etching chemistries, if there is no spontaneous etchingusing the chemistries selected and the above energy thresholds aremaintained.

In some embodiments, a relatively high pressure plasma is used. Thepressure of the chamber may be between about 30 mTorr and about 1000mTorr, for example about 100 to 500 mTorr or about 200 to 300 mTorr.This high pressure plasma includes a high concentration of inert species(for example, He, Ne, Ar, Kr, Xe, or combinations thereof) and lowconcentration of reactive species (for example, F-containing,Cl-containing, Br-containing, O-containing species.). Inert gasestypically generate more ions than other molecular gases in a standardplasma condition. In addition, a high concentration of inert species canensure the majority of ions (e.g., >99%) are non-reactive, and thereactive ion density is negligible.

While in high pressure plasma, the radicals or chemically reactivemolecules from reactive species are still enough for a sufficientchemisorption on the target material. The chemistry is selected to havechemisorption on the surface, but not enough reactivity for spontaneousetching without ion assistance. Ion energy (of inert species) is set ata value to be high enough to activate the surface after absorption ofthe chemically reactive species, but not enough for physical sputtering,similar to that of cyclic ALE. Plasma is delivered continuously suchthat both source power and bias power are continuously on. Etching isself-limiting because etching happens when the inert ions meet thechemisorbed, modified layer at the same site. Process conditions areselected such that inert ions or chemisorbed modified material on thesurface alone is insufficient to etch the material. In variousembodiments, etching is performed anisotropically. Anisotropic etch maybe achieved due to the directionality of inert ions delivered to asubstrate with a bias. In various embodiments, etching is alsoselective.

FIGS. 2A-B provide an example schematic illustration of a substratehaving features undergoing various operations in accordance withdisclosed embodiments. FIG. 2 shows a substrate including an underlayer201 and a target material layer 205 to be etched with an overlaying mask207. A continuous plasma is flowed, exposing the substrate to both aplasma of reactive species selected to modify the target material and aplasma of inert ions to remove the modified material in self-limitingreactions. The energy threshold for removing a layer of the materialmodified by the reactive species using the inert ions is less than theenergy threshold for sputtering the material on the substrate using theinert ions. The energy threshold for removing a layer of the materialmodified by the reactive species using the inert ions is also less thanthe energy threshold upon which inert ions have sufficient energy tobombard or sputter onto the surface of a mask layer over the targetlayer, thereby resulting in physical removal of mask material.

A well-controlled etch front allows a synergistic effect of reactiveradicals and inert ions to perform the etching, such that material isetched when the substrate is modified by reactive radicals and removedby inert ions, but not etched when material is modified by reactiveradicals but no inert ions are present, or when inert ions are presentbut material is not modified by reactive radicals. The process permitscontrolled, self-limiting anisotropic etching without alternatingbetween chemistries used to etch material on a substrate. The resultingsubstrate is depicted in FIG. 2B. Note that the mask 207 maintained agood profile without mask loss such that the sidewalls 207 a of the mask207 are still vertical. Additionally, the etched target layer 215 hassubstantially vertical sidewalls 215 a.

Processes described herein may involve the following describedoperations, depicted for example in the process flow of FIG. 3. In oneoperation (301), a reactive species may be chemisorbed onto the surfaceof material to be etched on a substrate. The reactive species mayconstitute reactive radicals or other chemistry generated by a plasmaand depends on the type of material being etched. Types of materials tobe etched using disclosed embodiments include carbon-containingmaterial, silicon-containing material, and metal-containing materials.One example of a carbon-containing material that may be etched usingdisclosed embodiments is amorphous carbon. Examples ofsilicon-containing materials that may be etched using disclosedembodiments include silicon, polysilicon, silicon-germanium, siliconoxide, silicon carbide, silicon-nitride, doped silicon carbide, dopedsilicon, and combinations thereof. Examples of metal-containingmaterials that may be etched using disclosed embodiments includeelemental metals such as tungsten and titanium, metal oxides such astitanium oxide, and metal nitrides.

For example, for etching carbon-containing material, the reactivespecies may include an oxygen-containing plasma, fluorine-containingplasma, chlorine-containing plasma, bromine-containing plasma, orcombinations thereof. Examples include Cl₂ and HBr. For example, in someembodiments, carbon-based materials may be etched using disclosedembodiments at a temperature less than about 50° C., such as about 20°C.

For etching a material that is primarily silicon, such assilicon-germanium or polysilicon, the reactive species may includefluorine-containing plasma, chlorine-containing plasma,bromine-containing plasma, or combinations thereof. Examples include Cl₂and HBr. For etching silicon oxide, the reactive species may includefluorocarbons, such as C_(x)F_(y), where x and y are integers, orC_(x)H_(y)F_(z), where x, y, and z are integers selected depending onthe material to be etched. For example, in some embodiments,silicon-based materials may be etched using disclosed embodiments at atemperature less than about 100° C., such as about 40° C.

In some embodiments, the reactive species may be used to etch ametal-based material on the substrate. For etching a material that is ametal oxide, such as titanium oxide, the reactive species may includehalogen-containing plasma, such as fluorine-containing plasma,bromine-containing plasma, and chlorine-containing plasma. One exampleof etching metal oxide using a chlorine-containing plasma involvesexposing the substrate to a gas, such as Cl₂, and igniting a plasma.Methods for etching metal oxides may be performed at a highertemperature than the temperature at which methods are performed foretching silicon-containing or carbon-containing materials. For example,in some embodiments, metal-based materials, e.g., metal oxides, may beetched using disclosed embodiments at a temperature greater than about80° C., such as about 120° C. It will be understood that substratetemperature or temperature as referred to herein indicates thetemperature at which a pedestal holding a substrate may be set.

The reactive species selected for chemisorbing onto the surface of thematerial to be etched does not spontaneously etch material on thesubstrate. In various embodiments, the reactive species is selected toalso not etch any mask or pattern on the surface of the substrate. Whenan energized inert ion reaches the chemisorbed or modified layer, thenthe chemisorbed layer obtains enough energy to activate the surface andform a nonvolatile by-product, which may then be removed from a chamberwhere the substrate is housed during etching operations.

In some embodiments, while the substrate is exposed to the reactivespecies, the substrate is also exposed to inert ions (303). In variousembodiments, the inert ions may be flowed to a chamber housing thesubstrate at a high concentration to dilute the presence of the reactivespecies and maintain a self-limiting etching process. Inert ions mayhave a high ionization rate. Examples include ions generated from He,Ne, Ar, Kr, Xe, or combinations thereof. In some embodiments, the ratioof inert ions to reactive species is controlled by operating at a highpressure, such as between about 30 mTorr and about 1000 mTorr. Operatingat a high pressure ensures enough reactive molecules and radicalsgenerated from the reactive species while suppressing overall iondensity of the inert ions to prevent damage to the substrate from theinert ions. In various embodiments, a bias voltage is set such that theion energy at which the inert ion would etch material is greater thanthe activation energy used to remove material of the chemisorbed layer,and while both energies are lower than the physical sputtering energy ofthe target material with inert ions, as described above with respect toFIG. 1.

Without being bound by a particular theory, it is believed that reactivespecies on the surface of the material to be etched may find a site andbe absorbed by the surface up to a few atomic layers. The adsorbed layerdoes not have enough energy to overcome the surface energy (e.g., itwill not be etched from the substrate) until an ion activates the localsite. Once an inert ion activates the local site, the activated siteforms a nonvolatile by-product, which may then diffuse into the chamberand be pumped out. However, if an ion reaches a surface that has noreactive chemicals absorbed, it would not have enough energy tophysically sputter the substrate, and hence damage to the substrate isprevented. Etching may thus be performed in a continuous fashion, whilestill maintaining self-limited reactions to control the etching profile.During etching, the reactive ion density is maintained at a very lowdensity (i.e. less than about 1% of the total ion density) and theplasma energy is also very low. The etch behavior may then be dominatedby inert ions, allowing the inert ions to activate the modified surfaceand etch material as the surface becomes modified by the reactivespecies.

One advantage of the disclosed embodiments is that there is an increasein throughput efficiency because gases are flowed continuously withoutswitching between gases (as is performed in cyclic ALE). Anotheradvantage is that disclosed embodiments can be easily controlled by afew plasma parameters, such as bias voltage, plasma power, plasmafrequency, gas flow rate and concentration, and chamber pressure.Disclosed embodiments generate a fast and well-controlled plasma whichmay be used to achieve low damage and high selectivity etching.

Furthermore, there are certain situations, like high aspect ratioetching, where radical diffusion becomes a major factor for the etchrate, aspect ratio dependence etching or through-pitch loading. Forthese applications, some embodiments may combine bias pulsing withhigher pressure, and low reactive concentration plasma.

For example, for etching high aspect ratio features, the gas mixture inthe etch chamber can be maintained with a low reactive ion concentrationfor chemisorption. Process conditions are controlled to ensure enoughtime for gas diffusion (which may range from μs to seconds). Biasvoltage may be on only after diffusion time is enough to reach bottom ofthe high aspect ratio features to form a chemisorption layer. A shortvoltage pulse may be used to deliver ions to remove this layer, anddiffusion-removal cycles may be repeated many times for high aspectratio etching. Since according to the removal energy thresholdtechniques of this disclosure ion energy is low so that only thechemisorption layers can be removed by ions, while in conventional etch,reactive ion etching is dominant and usually a higher ion energy isdesirable, performing the disclosed embodiments with bias pulsingresults in a substantial improvement in selectivity, compared toconventional etching with high voltages.

The disclosed gas mixing concept can be extended to more complicatedetching mechanisms and chemistries. For example, some C_(x)F_(y) orC_(x)H_(y)F_(z) etch chemistry or chemistry containing both etchant anddeposition species will involve some activation energy to etch targetmaterial. High voltage with reactive ions is helpful for etch rate, butit also causes more damage to the substrate, reduces mask selectivity,and sometimes causes sidewall attack by ion scattering. However, inertions with low energy can overcome some of the key challenges, becausewhen the ion energy is below the sputtering threshold, no ion damageoccurs. And if ion scattering happens, some energy is usually lost andmay not be able to activate the sidewall surface anymore. Anisotropicetching using disclosed embodiments is possible with infiniteselectivity to mask material. This can be applied to the core etch indouble patterning applications, along with many other patterning andgate etch applications, such as fabrication of FinFET structures, logicgates, and 3D NAND structures.

Apparatus

Disclosed embodiments may be performed in any suitable etching chamberor apparatus, such as the Kiyo® FX, available from Lam ResearchCorporation of Fremont, Calif. In some embodiments, an inductivelycoupled plasma (ICP) reactor may be used. Such ICP reactors have alsobeen described in U.S. Patent Application Publication No. 2014/0170853,filed Dec. 10, 2013, and titled “IMAGE REVERSAL WITH AHM GAP FILL FORMULTIPLE PATTERNING,” hereby incorporated by reference for the purposeof describing a suitable ICP reactor for implementation of thetechniques described herein. Although ICP reactors are described herein,in some embodiments, it should be understood that capacitively coupledplasma reactors may also be used. An example etching chamber orapparatus may include a chamber having chamber walls, a chuck forholding a substrate or wafer to be processed which may includeelectrostatic electrodes for chucking and dechucking a wafer and may beelectrically charged using an RF power supply, an RF power supplyconfigured to supply power to a coil to generate a plasma, and gas flowinlets for inletting gases as described herein. In some embodiments, anapparatus may include more than one chamber, each of which may be usedto etch, deposit, or process substrates. The chamber or apparatus mayinclude a system controller for controlling some or all of theoperations of the chamber or apparatus such as modulating the chamberpressure, inert gas flow, plasma power, plasma frequency, reactive gasflow (e.g., chlorine-containing gas, oxygen-containing gas,fluorine-containing gas, etc.); bias power, temperature, vacuumsettings; and other process conditions.

Apparatus

Inductively coupled plasma (ICP) reactors which, in certain embodiments,may be suitable for atomic layer etching (ALE) operations are nowdescribed. Such ICP reactors have also been described in U.S. PatentApplication Publication No. 2014/0170853, filed Dec. 10, 2013, andtitled “IMAGE REVERSAL WITH AHM GAP FILL FOR MULTIPLE PATTERNING,”hereby incorporated by reference in its entirety and for all purposes.Although ICP reactors are described herein, in some embodiments, itshould be understood that capacitively coupled plasma reactors may alsobe used.

FIG. 4 schematically shows a cross-sectional view of an inductivelycoupled plasma integrated etching and deposition apparatus 400appropriate for implementing certain embodiments herein, an example ofwhich is a Kiyo® reactor, produced by Lam Research Corp. of Fremont,Calif. The inductively coupled plasma apparatus 400 includes an overallprocess chamber 424 structurally defined by chamber walls 401 and awindow 411. The chamber walls 401 may be fabricated from stainless steelor aluminum. The window 411 may be fabricated from quartz or otherdielectric material. An optional internal plasma grid 450 divides theoverall process chamber 424 into an upper sub-chamber 402 and a lowersub-chamber 403. In most embodiments, plasma grid 450 may be removed,thereby utilizing a chamber space made of sub-chambers 402 and 403. Achuck 417 is positioned within the lower sub-chamber 403 near the bottominner surface. The chuck 417 is configured to receive and hold asemiconductor substrate or wafer 419 upon which the etching anddeposition processes are performed. The chuck 417 can be anelectrostatic chuck for supporting the wafer 419 when present. In someembodiments, an edge ring (not shown) surrounds chuck 417, and has anupper surface that is approximately planar with a top surface of thewafer 419, when present over chuck 417. The chuck 417 also includeselectrostatic electrodes for chucking and dechucking the wafer 419. Afilter and DC clamp power supply (not shown) may be provided for thispurpose. Other control systems for lifting the wafer 419 off the chuck417 can also be provided. The chuck 417 can be electrically chargedusing an RF power supply 423. The RF power supply 423 is connected tomatching circuitry 421 through a connection 427. The matching circuitry421 is connected to the chuck 417 through a connection 425. In thismanner, the RF power supply 423 is connected to the chuck 417.

Elements for plasma generation include a coil 433 is positioned abovewindow 411. In some embodiments, a coil is not used in disclosedembodiments. The coil 433 is fabricated from an electrically conductivematerial and includes at least one complete turn. The example of a coil433 shown in FIG. 4 includes three turns. The cross-sections of coil 433are shown with symbols, and coils having an “X” extend rotationally intothe page, while coils having a “●” extend rotationally out of the page.Elements for plasma generation also include an RF power supply 441configured to supply RF power to the coil 433. In general, the RF powersupply 441 is connected to matching circuitry 439 through a connection445. The matching circuitry 439 is connected to the coil 433 through aconnection 443. In this manner, the RF power supply 441 is connected tothe coil 433. An optional Faraday shield 449 is positioned between thecoil 433 and the window 411. The Faraday shield 449 is maintained in aspaced apart relationship relative to the coil 433. The Faraday shield449 is disposed immediately above the window 411. The coil 433, theFaraday shield 449, and the window 411 are each configured to besubstantially parallel to one another. The Faraday shield 449 mayprevent metal or other species from depositing on the window 411 of theprocess chamber 424.

Process gases (e.g. reactive species or precursors, reducing agents,carrier gases, halogen-containing gases, chlorine, inert gases, such ashelium, argon, etc.) may be flowed into the process chamber through oneor more main gas flow inlets 460 positioned in the upper sub-chamber 402and/or through one or more side gas flow inlets 470. Likewise, thoughnot explicitly shown, similar gas flow inlets may be used to supplyprocess gases to a capacitively coupled plasma processing chamber. Avacuum pump 440, e.g., a one or two stage mechanical dry pump and/orturbomolecular pump, may be used to draw process gases out of theprocess chamber 424 and to maintain a pressure within the processchamber 424. For example, the vacuum pump 440 may be used to evacuatethe lower sub-chamber 403 during a purge operation of ALE. Avalve-controlled conduit may be used to fluidically connect the vacuumpump to the process chamber 424 so as to selectively control applicationof the vacuum environment provided by the vacuum pump. This may be doneemploying a closed-loop-controlled flow restriction device, such as athrottle valve (not shown) or a pendulum valve (not shown), duringoperational plasma processing. Likewise, a vacuum pump and valvecontrolled fluidic connection to the capacitively coupled plasmaprocessing chamber may also be employed.

During operation of the apparatus 400, one or more process gases may besupplied through the gas flow inlets 460 and/or 470. In certainembodiments, process gas may be supplied only through the main gas flowinlet 460, or only through the side gas flow inlet 470. In some cases,the gas flow inlets shown in the figure may be replaced by more complexgas flow inlets, one or more showerheads, for example. The Faradayshield 449 and/or optional grid 450 may include internal channels andholes that allow delivery of process gases to the process chamber 424.Either or both of Faraday shield 449 and optional grid 450 may serve asa showerhead for delivery of process gases. In some embodiments, aliquid vaporization and delivery system may be situated upstream of theprocess chamber 424, such that once a liquid reactant or precursor isvaporized, the vaporized reactant or precursor is introduced into theprocess chamber 424 via a gas flow inlet 460 and/or 470.

Radio frequency power is supplied from the RF power supply 441 to thecoil 433 to cause an RF current to flow through the coil 433. The RFcurrent flowing through the coil 433 generates an electromagnetic fieldabout the coil 433. The electromagnetic field generates an inductivecurrent within the upper sub-chamber 402. The physical and chemicalinteractions of various generated ions and radicals with the wafer 419etch features of and deposit layers on the wafer 419.

Volatile etching and/or deposition byproducts may be removed from thelower sub-chamber 403 through port 422. The chuck 417 disclosed hereinmay operate at elevated temperatures ranging between about 10° C. andabout 250° C. The temperature will depend on the process operation andspecific recipe.

Apparatus 400 may be coupled to facilities (not shown) when installed ina clean room or a fabrication facility. Facilities include plumbing thatprovide processing gases, vacuum, temperature control, and environmentalparticle control. These facilities are coupled to apparatus 400, wheninstalled in the target fabrication facility. Additionally, apparatus400 may be coupled to a transfer chamber that allows robotics totransfer semiconductor wafers into and out of apparatus 400 usingtypical automation.

In some embodiments, a system controller 430 (which may include one ormore physical or logical controllers) controls some or all of theoperations of a process chamber 424. The system controller 430 mayinclude one or more memory devices and one or more processors. Forexample, the memory may include instructions to alternate between flowsof modification chemistry such as a chlorine-containing modificationchemistry and a removal gas such as argon, or instructions to ignite aplasma or apply a bias. For example, the memory may include instructionsto set the bias at a power between about 0V and about 200V during someoperations. In some embodiments, the apparatus 400 includes a switchingsystem for controlling flow rates and durations when disclosedembodiments are performed. In some embodiments, the apparatus 400 mayhave a switching time of up to about 500 ms, or up to about 750 ms.Switching time may depend on the flow chemistry, recipe chosen, reactorarchitecture, and other factors.

In some embodiments, disclosed embodiments can be integrated on a MSSD(Multi-Station-Sequential-Deposition) chamber architecture in which oneof deposition stations can be replaced by an ALE station to allow anintegrated deposition/etch/deposition process using a similar chemistryfor better fill and faster throughput capability.

In some implementations, the system controller 430 is part of a system,which may be part of the above-described examples. Such systems caninclude semiconductor processing equipment, including a processing toolor tools, chamber or chambers, a platform or platforms for processing,and/or specific processing components (a wafer pedestal, a gas flowsystem, etc.). These systems may be integrated with electronics forcontrolling their operation before, during, and after processing of asemiconductor wafer or substrate. The electronics may be integrated intothe system controller 430, which may control various components orsubparts of the system or systems. The system controller 430, dependingon the processing parameters and/or the type of system, may beprogrammed to control any of the processes disclosed herein, includingthe delivery of processing gases, temperature settings (e.g., heatingand/or cooling), pressure settings, vacuum settings, power settings,radio frequency (RF) generator settings, RF matching circuit settings,frequency settings, flow rate settings, fluid delivery settings,positional and operation settings, wafer transfers into and out of atool and other transfer tools and/or load locks connected to orinterfaced with a specific system.

Broadly speaking, the system controller 430 may be defined aselectronics having various integrated circuits, logic, memory, and/orsoftware that receive instructions, issue instructions, controloperation, enable cleaning operations, enable endpoint measurements, andthe like. The integrated circuits may include chips in the form offirmware that store program instructions, digital signal processors(DSPs), chips defined as application specific integrated circuits(ASICs), and/or one or more microprocessors, or microcontrollers thatexecute program instructions (e.g., software). Program instructions maybe instructions communicated to the controller in the form of variousindividual settings (or program files), defining operational parametersfor carrying out a particular process on or for a semiconductor wafer orto a system. The operational parameters may, in some embodiments, bepart of a recipe defined by process engineers to accomplish one or moreprocessing steps during the fabrication or removal of one or morelayers, materials, metals, oxides, silicon, silicon dioxide, surfaces,circuits, and/or dies of a wafer.

The system controller 430, in some implementations, may be a part of orcoupled to a computer that is integrated with, coupled to the system,otherwise networked to the system, or a combination thereof. Forexample, the controller may be in the “cloud” or all or a part of a fabhost computer system, which can allow for remote access of the waferprocessing. The computer may enable remote access to the system tomonitor current progress of fabrication operations, examine a history ofpast fabrication operations, examine trends or performance metrics froma plurality of fabrication operations, to change parameters of currentprocessing, to set processing steps to follow a current processing, orto start a new process. In some examples, a remote computer (e.g. aserver) can provide process recipes to a system over a network, whichmay include a local network or the Internet. The remote computer mayinclude a user interface that enables entry or programming of parametersand/or settings, which are then communicated to the system from theremote computer. In some examples, the system controller 430 receivesinstructions in the form of data, which specify parameters for each ofthe processing steps to be performed during one or more operations. Itshould be understood that the parameters may be specific to the type ofprocess to be performed and the type of tool that the controller isconfigured to interface with or control. Thus as described above, thesystem controller 430 may be distributed, such as by including one ormore discrete controllers that are networked together and workingtowards a common purpose, such as the processes and controls describedherein. An example of a distributed controller for such purposes wouldbe one or more integrated circuits on a chamber in communication withone or more integrated circuits located remotely (such as at theplatform level or as part of a remote computer) that combine to controla process on the chamber.

Without limitation, example systems may include a plasma etch chamber ormodule, a deposition chamber or module, a spin-rinse chamber or module,a metal plating chamber or module, a clean chamber or module, a beveledge etch chamber or module, a physical vapor deposition (PVD) chamberor module, a chemical vapor deposition (CVD) chamber or module, an ALDchamber or module, an ALE chamber or module, an ion implantation chamberor module, a track chamber or module, and any other semiconductorprocessing systems that may be associated or used in the fabricationand/or manufacturing of semiconductor wafers.

As noted above, depending on the process step or steps to be performedby the tool, the controller might communicate with one or more of othertool circuits or modules, other tool components, cluster tools, othertool interfaces, adjacent tools, neighboring tools, tools locatedthroughout a factory, a main computer, another controller, or tools usedin material transport that bring containers of wafers to and from toollocations and/or load ports in a semiconductor manufacturing factory.

FIG. 5 depicts a semiconductor process cluster architecture with variousmodules that interface with a vacuum transfer module 538 (VTM). Thearrangement of transfer modules to “transfer” wafers among multiplestorage facilities and processing modules may be referred to as a“cluster tool architecture” system. Airlock 530, also known as aloadlock or transfer module, is shown in VTM 538 with four processingmodules 520 a-520 d, which may be individual optimized to performvarious fabrication processes. By way of example, processing modules 520a-520 d may be implemented to perform substrate etching, deposition, ionimplantation, wafer cleaning, sputtering, and/or other semiconductorprocesses. In some embodiments in accordance with this disclosure,modification by reactive species and exposure to inert ions for materialetch and removal are performed in the same module. Airlock 530 andprocess module 520 may be referred to as “stations.” Each station has afacet 536 that interfaces the station to VTM 538. Inside each facet,sensors 1-18 are used to detect the passing of wafer 526 when movedbetween respective stations.

Robot 522 transfers wafer 526 between stations. In one embodiment, robot522 has one arm, and in another embodiment, robot 522 has two arms,where each arm has an end effector 524 to pick wafers such as wafer 526for transport. Front-end robot 532, in atmospheric transfer module (ATM)540, is used to transfer wafers 526 from cassette or Front OpeningUnified Pod (FOUP) 534 in Load Port Module (LPM) 542 to airlock 530.Module center 528 inside process module 520 is one location for placingwafer 526. Aligner 544 in ATM 540 is used to align wafers.

In an exemplary processing method, a wafer is placed in one of the FOUPs534 in the LPM 542. Front-end robot 532 transfers the wafer from theFOUP 534 to an aligner 544, which allows the wafer 526 to be properlycentered before it is etched or processed. After being aligned, thewafer 526 is moved by the front-end robot 532 into an airlock 530.Because airlock modules have the ability to match the environmentbetween an ATM and a VTM, the wafer 526 is able to move between the twopressure environments without being damaged. From the airlock module530, the wafer 526 is moved by robot 522 through VTM 538 and into one ofthe process modules 520 a-520 d. In order to achieve this wafermovement, the robot 522 uses end effectors 524 on each of its arms. Oncethe wafer 526 has been processed, it is moved by robot 522 from theprocess modules 520 a-520 d to an airlock module 530. From here, thewafer 526 may be moved by the front-end robot 532 to one of the FOUPs534 or to the aligner 544.

It should be noted that the computer controlling the wafer movement canbe local to the cluster architecture, or can be located external to thecluster architecture in the manufacturing floor, or in a remote locationand connected to the cluster architecture via a network. A controller asdescribed above with respect to FIG. 4 may be implemented with the toolin FIG. 5.

EXPERIMENTAL Experiment 1

FIG. 6 shows a plot of reference data of ion density and pressure forvarious inert gases. Data was obtained by flowing the gases at differentpressures into an etch tool with a simple inert or reactive gas.Normalized ion density vs pressure for 200 sccm flow of Ar, He, Cl₂,HBr, O₂, N₂ and CF₄, with a plasma power of 1500 W is shown. Asindicated in the Figure, the ion density decreases with higher pressurefor many gases, and Ar or He generates much higher ion density thanother molecular gases.

Experiment 2

An experiment was conducted on a substrate including an underlayer and atarget carbon-containing layer with an overlying mask. The substrate washoused in a chamber having a chamber pressure of 200 mTorr. Thesubstrate was exposed for 30 seconds to a plasma generated using aninductively coupled plasma power set at 1500 W using 1500 sccm heliumand 5 sccm O₂ at a temperature of 20° C. while applying a bias of 50Vb.The process etched 35.73 nm of the carbon layer, and the etchedcarbon-containing target layer had substantially vertical sidewalls.Additionally, the mask maintained a good profile without mask loss suchthat the sidewalls of the mask remained vertical.

Experiment 3

An experiment was conducted on a substrate including titanium oxidespacers in a carbon-containing layer over a substrate. The substrate washoused in a chamber having a chamber pressure of 200 mTorr. Thesubstrate was exposed for 100 seconds to a plasma generated using aninductively coupled plasma power set at 1500 W using a 1500 sccm heliumand 10 sccm Cl₂ mixture at a temperature of 120° C. while applying abias of 50Vb. Titanium oxide spacers were anisotropically etched in thisprocess and the resulting substrate maintained a good profile withoutmask loss or sidewall etching such that the sidewalls of the maskremained vertical and no undercut was observed.

Experiment 4

An experiment was conducted on a silicon-based substrate with anoverlying photoresist mask. The substrate was housed in a chamber havinga chamber pressure of 250 mTorr. The substrate was exposed for 10seconds to a plasma generated using an inductively coupled plasma powerset at 1000 W using 1500 sccm helium and 20 sccm CF₄ at a temperature of40° C. while applying a bias of 50Vb. Features in the substrate wereanisotropically etched in this process and the resulting substratemaintained a good profile without sidewall etching such that thesidewalls of the etched features and mask remained vertical and noundercut was observed.

CONCLUSION

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, it will be apparent thatcertain changes and modifications may be practiced within the scope ofthe appended claims. It should be noted that there are many alternativeways of implementing the processes, systems, and apparatus of thepresent embodiments. Accordingly, the present embodiments are to beconsidered as illustrative and not restrictive, and the embodiments arenot to be limited to the details given herein.

What is claimed is:
 1. A method of etching a material of a substrate,the method comprising: exposing a substrate in a processing chamber to aplasma-generated reactive species, and while the substrate is exposed tothe plasma-generated reactive species, also exposing the substrate toplasma-generated inert ions to remove a material exposed on thesubstrate using self-limiting reactions, wherein an energy threshold forremoving a layer of the material modified by the reactive species usingthe inert ions is less than an energy threshold for sputtering thematerial exposed on the substrate using the inert ions.
 2. The method ofclaim 1, wherein exposure of the substrate to the reactive speciesmodifies the exposed material of the substrate, and the inert ionsgenerated by the plasma remove the modified substrate material, therebyetching the material of the substrate.
 3. The method of claim 1,wherein, during the exposure of the substrate to the reactive speciesand inert ions, the plasma is delivered continuously such that bothsource power and bias power are continuously on while etching thematerial of the substrate.
 4. The method of claim 3, wherein theconcentration of the inert ions present in the processing chamber duringthe etch is greater than 99% of all chemical species in the chamber,while the concentration of reactive species is less than about 1%. 5.The method of claim 1, further wherein a mask layer overlies thematerial of the substrate to be etched, and the energy threshold forremoving a layer of the material modified by the reactive species usingthe inert ions is less than the energy threshold upon which the inertions have sufficient energy to bombard or sputter onto the surface of amask layer over the target layer, thereby resulting in physical removalof mask material.
 6. The method of claim 1, wherein processing chamberpressure is between about 30 mTorr and about 1000 mTorr.
 7. The methodof claim 6, wherein processing chamber pressure is between about 100mTorr and about 500 mTorr.
 8. The method of claim 7, wherein processingchamber pressure is between about 200 mTorr and about 300 mTorr.
 9. Themethod of claim 1, wherein the ion density of reactive ions, that arereactive to etch unmodified material on the substrate, is negligible.10. The method of claim 1, wherein the material of a substrate to beetched is carbon-based.
 11. The method of claim 10, wherein thecarbon-containing material to be etched is amorphous carbon.
 12. Themethod of claim 11, wherein the reactive species includes speciesselected from the group consisting of an oxygen-containing plasma,fluorine-containing plasma, chlorine-containing plasma,bromine-containing plasma, or combinations thereof.
 13. The method ofclaim 1, wherein the material of a substrate to be etched issilicon-based.
 14. The method of claim 13, wherein thesilicon-containing material to be etched is selected from the groupconsisting of silicon, polysilicon, silicon-germanium, silicon oxide,silicon carbide, silicon-nitride, doped silicon carbide, doped silicon,and combinations thereof.
 15. The method of claim 14, wherein thereactive species includes species selected from the group consisting ofa fluorine-containing plasma, chlorine-containing plasma,bromine-containing plasma, or combinations thereof.
 16. The method ofclaim 1, wherein the material of a substrate to be etched ismetal-based.
 17. The method of claim 16, wherein the metal-containingmaterial to be etched is selected from the group consisting elementalmetals tungsten and titanium, metal oxide, titanium oxide, metalnitrides, and combinations thereof.
 18. The method of claim 17, whereinthe reactive species includes species selected from the group consistingof a fluorine-containing plasma, chlorine-containing plasma,bromine-containing plasma, or combinations thereof.
 19. The method ofclaim 1, wherein the inert ions include ions generated from He, Ne, Ar,Kr, Xe, or combinations thereof.